capture: answer the stop before summarising, and always leave a note

capture_stop held the IPC request open for the whole map reduce, up to
twenty minutes. A voice turn that says "хватит" waited for forty model
calls before Maven said anything. Stop now returns the transcript and the
summary runs on a goroutine in the daemon's WaitGroup, on the daemon
context so a client that hung up does not cancel the only readable record
of the meeting.

With no summary and save_transcript false, writeNotes wrote nothing at
all: an hour of meeting left a blob that prunes in seven days and no
trace in the note store. The transcript is written instead when the
summary is missing. That flag decides whether the verbatim record is kept
in addition to a summary, not whether the meeting is remembered.

The wire carries the session token now, and the contract comments say
what the code does: the summary is usually absent from the stop
response, and re running a stored blob is a manual job because no method
takes a blob id. The save_transcript comment says the cost is recall
corpus rather than disk.

Found in review of #73.

cmd/mavend/main.go

@@ -385,7 +385,7 @@ func run(args []string) error {
 		// The meeting recorder (Vikunja #253) shares that blob store and its
 		// retention loop. Off unless a capture block enables it, in which case
 		// all four capture methods answer ErrUnknownMethod.
-		wireCapture(srv, keeper, st, voiceW, phr, cfg)
+		wireCapture(ctx, &wg, srv, keeper, st, voiceW, phr, cfg)
 		// Voice identification (Vikunja #255). Enrolment plumbing only until a
 		// speaker-embedding model exists on disk; off entirely without a speaker
 		// block, so no wire path takes a voiceprint on a default box.
@@ -561,7 +561,7 @@ func run(args []string) error {
 			wireMailIntake(srv, st, phr, cfg, evBus)
 			wireModelSwap(srv, phr, cfg)
 			keeper := wireVision(ctx, &wg, srv, st, embedderOf(voiceW), cfg)
-			wireCapture(srv, keeper, st, voiceW, phr, cfg)
+			wireCapture(ctx, &wg, srv, keeper, st, voiceW, phr, cfg)
 			// Voice identification (Vikunja #255). Enrolment plumbing only until a
 			// speaker-embedding model exists on disk; off entirely without a speaker
 			// block, so no wire path takes a voiceprint on a default box.